The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Powertrain systems employing electric machines for tractive torque derate motor torque based upon a single control parameter, e.g., motor temperature, with tractive torque effort derated as a function of the motor temperature to avoid reduced service life of the electric machine. In one embodiment, torque derating occurs in a temperature range between a minimum temperature for derating, e.g., 170° C. and a maximum permissible operating temperature, e.g., 190° C. This includes permitting maximum motor torque at motor temperatures below the minimum temperature for derating, linearly derating the motor torque as motor temperature increases thereabove, e.g., from 170° C. to 190° C. and permitting zero motor torque output, i.e., prohibiting motor torque output when the motor temperature reaches the maximum permissible operating temperature.
Under one known severe driving schedule, an electric machine can spend a majority of its operating time operating at motor temperatures slightly less than the minimum temperature for derating, e.g., at approximately 160° C. A motor control approach employing motor temperature as a single control parameter permits indefinite operation of an electric machine at motor temperatures that are slightly below the minimum temperature for derating, affecting its service life. Furthermore, a motor control approach employing motor temperature as a single control parameter prohibits short-duration high temperature excursions even though such excursions may not affect service life.